Low-pressure inking system and ink therefor

ABSTRACT

A low-pressure inking system for oscillographic pen recorders is disclosed in which the pen is biased against the recording medium (paper) at low pressure so that special pen motors are unnecessary. The system includes a low-viscosity aqueous ink containing ethylene glycol monomethyl ether in a concentration of about 20-35 percent, a coloring agent and a soluble resin such as polyvinylpyrrolidone or polyethylene oxide. Low stylus tip pressure may be used so that the pen motor driving torque required to obtain good writing without hysteresis is substantially less than with conventional pressurized ink writing systems and retrofitting of conventional capillary recorders is made possible.

Siegelman et al.

' [451 Dec.24, 1974 LOW-PRESSURE INKING SYSTEM AND INK THEREFOR IInventors: Abe Siegelman, Morton Grove;

Robert N. Quoss, Clarendon Hills; Raymond M. Pawlak, Addison, all

of I11.

Beckman Instruments, Inc., Fullerton, Calif.

Filed: Aug. 20, 1973 Appl. No.: 389,682

Related US. Application Data Continuation-impart of Ser. No. 263,699,June 16, 1972, which is a continuation of Ser, No. 50,652, June 29,1970, abandoned.

Assignee:

US. Cl 106/22, 106/19, 106/20, 260/296 E Int. Cl C09d 11/00 Field ofSearch 106/22, 20, 19; 260/37 AL, 260/296 E References Cited UNITEDSTATES PATENTS ll/l969 Forsyth, Jr 106/22 3,705,043 12/1972 Zabiak106/20 Primary Examiner-Morris Liebman Assistant ExaminerE. Suzanne ParrAttorney, Agent, or Firm-Mason, Kolehmainen, Rathburn & Wyss [57]ABSTRACT A low-pressure inking system for oscillographic pen recordersis disclosed in which the pen is biased against the recording medium(paper) at low pressure so that special pen motors are unnecessary. Thesystem includes a low-viscosity aqueous ink containing ethylene glycolmonomethyl ether in a concentration of about 20-35 percent, a coloringagent and a soluble resin such as polyvinylpyrrolidone or polyethyleneoxide. Low stylus tip pressure may be used so that the pen motor drivingtorque required to obtain good writing without hysteresis issubstantially less than with conventional pressurized ink writingsystems and retrofitting of conventional capillary recorders is madepossible.

4 Claims, 1 Drawing Figure LOW-PRESSURE INKING SYSTEM AND INK THEREFORCROSS-REFERENCE TO RELATED APPLICATIONS GENERAL DESCRIPTION OF INVENTIONThis invention relates to an improved ink and hydrostatic inking systemuseful in oscillographic pen recorders and the like. In particular, itrelates to a lowpressure hydrostatic inking system including alowviscosity ink under a low hydrostatic head.

In the past the usual pen recorder of the oscillographic type used aliquid ink to write on a moving paper chart. This system had manyadvantages over electric writing and photographic systems in that it wasrelatively inexpensive and was instantaneous. However, it for years hassuffered from many disadvantages. These disadvantages were sufficientlygreat that for many applications electric writing is used in spite ofthe high cost of the record medium; photographic devices are employedeven though the film is expensive and has to be developed over a periodof time; special ultraviolet recorders are used; and chemical recordersare used with heat; and straight heat recorders are used.

The chief disadvantages of the inking system as it was heretofore knownhave been due to the liquid ink which was used. This liquid ink had todry quickly after it was applied to the moving record medium becauseotherwise it would smear as the paper was rolled up and the operatorwould often touch the wet ink causing loss of accuracy of the record,unsightly records, etc. The quick drying quality which was sohighlydesirable when the ink was applied to the chart paper was a tremendousdisadvantage when the pen recorder was not used for a while, as itcaused clogging of the small hole in the tip of the pen and consequentlythe pen often would not write when the instrument was first started.Systems were employed to force the ink out of the pen tip to clear thepassageway so that the capillary forces involved in the pen and in thetube connecting the liquid ink supply to the pen would thereafter supplyadequate ink for writing on the moving paper.

Another disadvantage inherent in the liquid ink system is that therapidly oscillating pen tip would often throw drops of ink around theroom.

A further disadvantage of prior systems is that certain of them (e.g.,Brown Re. 25,792, Dec. l, 1964) have required high-viscosity ink whichhad to be forced through the equipment under relatively high pressure.Such systems necessarily included pumps or pressurized gases whichforced the ink through ducts to tubular pens. Generally the tubular penswere arranged so that the pen tips were held against record paper orsimilar material with substantial biasing force, and the ink underrelatively high pressure was extruded against the record paper andsheared off as the pen tip moved relative to the latter. These systemshave required special high-powered pen motors to move the pens which arebiased against the record media.

The system of the present invention is an inking mechanism, having allthe advantages of the previous liquid ink systems in that it isrelatively inexpensive and is instantaneous, and in addition the newsystem obviates the disadvantages inherent in such liquid ink systerns.

An object of the present invention is to provide a low-pressurehydrostatic inking system which does not require high viscosity ink,high pressure ink-supplying equipment, high biasing force on the pen tipor a special pen motor to activate the biased pen.

A further object of the invention is to provide low viscosity inks foruse in such low-pressure hydrostatic inking systems.

Another object is to provide a low-viscosity ink which has adequatecapillary strength suitable for use in low-pressure inking systems,which is rapidly absorbed by most types of paper, and which does notsmear or feather on the'paper.

Still another object is to provide a low-viscosity ink which is stableonstorage at high and low pressures, does not bleed from pen tips, evenwhen left in contact with paper for extended times.

A still further object is to provide a low-viscosity ink which does notsplatter when the pen is moving rapidly or erratically. 7

These and other objects are apparent from and are achieved in accordancewith the following disclosure, taken in connection with the attacheddrawing in which the single FIGURE illustrates a typical low-pressureinking system arrangement of the present invention.

Referring now to the drawing, the low-pressure, low viscosity inkingsystem of the present invention is herein illustrated as comprising apen motor, indicated generally at 10, which is arranged to be energizedby any suitable electrical signal and provides rotation of the outputshaft 12 thereof in proportion to the amplitude of said electrical inputsignal. A pen arm 14 is pivotally mounted on a carriage 16 secured tothe upper end of the shaft 12 and is provided with a right angle pen tipportion 18 which is biased against the chart paper 20 by means of thespring clip member 22. Upon rotation of the shaft 12 the pen tip 18 ismoved transversely of the paper 20 and ink stored in the chamber 24 isdrawn out of this chamber through the tubing 26 and pen conduit 28 sothat a fine, brilliant line is made on the paper 20 corresponding to theelectrical input signal. Preferably, the tubing 26 is of polyethylene orbutyl rubber and the conduit 28 is of stainless steel or inconel toavoid undesired interaction with and possible clogging of the inkdescribed in detail hereinafter.

The vertical position of the chamber 24 may be ad-- justed by means of aclamp member 30 to provide any desired gravimetric head but it ispointed out that the ink described hereinafter will function.satisfactorily even under negative pressure, i.e., when the level ofink in the chamber 24 is below the pen tip 18.

In the illustrated embodiment the chart paper 20 is of the Z-fold type,a pack 32 of this type of paper being stored below the writing table 34and being pulled tautly over the surface of this table by any suitabledrive means. It is pointed out, however, that the'chart paper may be ofthe roll type without folds. Also, in accordance with an importantfeature of the invention, the ink described hereinafter may be used withchart paper 20 of either the coated or uncoated type. When used withlow-cost, uncoated paper the ink does not splatter and yet provides ahigh contrast, brilliant record trace which is comparable to thatobtained with coated paper except for the high gloss of the paperitself. The inking system of the present invention is also particularlysuited for use with coated paper of the Z- fold type because the lowstylus pressure requirements of the pen tip 18 and the particularcharacteristics of the ink described hereinafter accomodate the foldportions of this type of paper and the loose paper fibers which areusually present therein without clogging of the pen tip or interferingwith the free flow of ink therefrom. A jewel pen tip 18 having a roundedbottom edge is preferably employed with this type of paper to let thepen tip slide over the paper folds easily. Furthermore, the fact thatthe spring clip 22 need exert only a slight biasing force on the pen tip18 means that the torque requirements imposed on the pen motor arerelatively small, as compared to high-pressure, highviscosity inkingsystems such as shown in Brown Reissue Pat. No. 25,692, and henceconventional capillary discovered that low'viscosity (i.e., 1-30 cps.)inks containing a major proportion of water and about -35 percent byweight ethylene glycol monomethyl ether and a water-soluble resin areparticularly desirable in low-pressure inking systems. Such inks do notspatter during operation of the equipment and effectively dry veryrapidly, thus avoiding feathering and smearing, and can be used oncoated recording paper, such as Kromekote paper, Trycite paper andsimilar high gloss paper, uncoated papers such as sulfite and sulfatepapers, tissue paper, newsprint, tracing vellum, and films of polyamide.

This ink has been shown to write effectively on literally every type ofpaper produced today. The paper stock can include synthetic fibersincluding the chemically modified fibers, cotton or other cellulosics,bagasse, any kind of mineral fibers such as asbestos, mica, etc. Thestock can be mechanically or chemically digested or both-it can besulfite or sulfate. The stock can be highly beaten and fibrillated evento the point of producing a highly fibrillated and hydrated glassinepaper. The ink has been shown effective on glassines, and tracingvellum. The synthetic polymer fibers made into paper are also suitableto be written on with the new ink. It does not matter what type ofcommon beater additives have been used in producing the papers writtenon with the EM ink disclosed herein. We are therefore in no way limitedby the type of paper used with our oscillographic pen recorder. Becauseof this, substantial savings can be appreciated while achievingaccurracy even greater than that heretofore known with oscillographicpen recorders.

Aqueous inks which are pen recorded on papers having water penetrabilityhave a tendency to bleed (the spreading of the ink in a directiondifferent from the direction of pen travel). The accurracy of anoscillographic pen recorder depends upon whether the inked recordreflects the exact position of the pen tip during paper travel. When theink bleeds, it is difficult if not impossible to determine exactly wherethe pen tip touched the paper in those places where bleeding occurred,making the chart inaccurrate.

Ethylene glycol monomethyl ether (EM) is a unique ink solvent in thatwhen used in aqueous inks in the concentration of 20-35 percent, byweight bleeding does not occur even on uncoated papers. These uncoatedpapers may or may not be internally sized, but preferably they havebeen. Further this solvent in a 20-35 percent by weight concentrationalso gives extremely clear brilliant unbleeding lines on highly glossycoated papers (coating makes the paper have a smoother surfaceespecially when calendared after a coating as well known in thepapermaking art these coating agents cause a decrease in'waterpenetrability and a filling of the'fiber to fiber interstices andtherefore a higher smoothness and gloss). One such paper is.manufactured by coating with clay prior to calendaring (i.e., Kromecotemade by Champion Papers of Hammilton, Ohio). Pen dye using EM as thesolvent is therefor very conveniently and economically used on the lessexpensive uncoated papers (sized or unsized) and it gives more brilliantlines of more even width throughout than the ink solvents now used inthe art.

It has been found that if too low a EM concentration is used, the inkwill bleed or spread on the paper especially on the coated paper. Forexample, when used at 12-14 percent concentration as are the glycerins(common prior art solvents see the Forsyth U.S. Pat. No. 3,477,862)bleeding occurs. When EM is used in a concentration of greater than 35percent, feathering occurs on the uncoated paper. It has been found,however, that in the 20-35 percent by weight concentration, EM givesclear brilliant lines of substantially constant thickness throughout theentire oscilliscopic path, without bleeding on both coated and uncoatedpapers.

It is quite surprising that EM ink writes on both coated and uncoatedpapers without bleeding since the prior art glycols cause bleeding andsince even the ethylene glycol lower alkyl ethers cause bleeding onuncoated papers.

Moreover, such low viscosity inks can be fed to the pen tip underordinary gravity pressure (0-8 inches), thus avoiding pumps and otherpressurizing equipment called for by prior inking systems, and they caneven be used at zero or negative pressure at lower writing rates byreason of their capillary strength. As a consequence, low styluspressure (1-3 grams) is suitable to produce sharp recordings and hightorque pen servomotors and position transducers are unnecessary.

The preferred viscosity of the ink is 5-10 cps. at 20C. This ink can besupplied to the pen tip under pressures of less than A psig. Pressuresup to 2 psig. are satisfactory for all of the inks described herein.

The low viscosity ink contains a major proportion of water, and a watersoluble dye is used in the ink of a type which will not greatly increaseviscosity. The other essential components are ethylene glycol monomethylether which constitutes'from about 20 to 35 percent of the weight of theink, and a water-soluble resin such as polyvinyl-pyrrolidone orpolyethylene oxide.

The ink contains sufficient water-soluble dye to produce a coloredmarking on paper or similar sheet material. Many such dyes are wellknown and can be selected on the basis of desired color, stability andcompatibility with the other ink components.

A small percentage of a water-soluble resin such as polyvinylpyrrolidone(PVP) is used to prevent splattering at high speed pen travel. PVP isusually present in an amount from about 0.1 to 5 percent of the weightof the ink. It prevents breaking of the capillary in the pen tip,reduces friction in the pen and tubing, keeps the ink cohesive, aids inholding the dye in solution,

and prevents bleeding of the ink from the pen tip when the system is notin use. Polyethylene oxide serves the same purposes and can besubstituted in smaller 7 amounts for PVP. Usually the amount ofpolyethylene volatile, water-soluble amines canbe used, such asdiethanolamine, propanolamine and the like. However,

slightly acidic inks with pHs between 5 and 7 are operative. Some inkswhich are slightly acidic (e.g., pH 4) are suitable but usually slightlyalkaline inks are preferred.

It has been found in some cases that the addition of a small amount ofphenol or similar agent reduces or prevents the growth of bacteria, moldand other microorganisms in the ink. These materials need be presentonly in low effective amounts (e.g. 0.01 to 0.5 percent). Usually theyare not required because the glycol ether suppresses the growth ofbacteria and mold.

The following examples illustrate formulations of suitable inks for theinking system of this application.

EXAMPLE 1 A low-viscosity ink suitable for both uncoated sulfite andcoated (i.e., Kromecote) papers was made of the following materials:

150 g. water (deionized) 50 g. ethylene glycol monomethyl ether 6 g.Pontacyl violet 84B 0125 g. polyethylene oxide WSR-30l (approx. mol.

The polyethylene oxide was dissolved in the water, followed by theglycol ether and the dye. An intense violet ink, pH 8, viscosity 7 cps,was produced.

EXAMPLE 2 A green ink was produced by the procedure of Example 1 fromthe following:

150 g. water 50 g. ethylene glycol monomethyl ether 6 g. Keco acid green4LEX 0.125 g. polyethylene oxide WSR-30I I 6 It had pH 6.4 and viscosity7 cps.

EXAMPLE 3 A red ink was produced by the procedure of Example 2 from thefollowing:

450 g. water g. ethylene glycol monomethyl ether 18 g. Pontacyl carmine'26 0.375 g. polyethylene oxide WSR-30l lt had pH 9.7 and viscosity 6cps.

EXAMPLE 4 A violet ink was produced from the following materials:

450 g. water 150 g. ethylene glycol monomethyl ether 0.375 g.polyethylene oxide WSR-30l 12 g. Crystal violet 6B conc.

It was adjusted to pH 7.9 with two drops of ethanolamine; viscosity 6.5cps.

EXAMPLE 5 The following formula produces a suitable red ink:

150 g. water 50 g. ethylene glycol monomethyl ether 6 g. Keco acid red6BC 0.125 g. polyethylene oxide WD R-ZSO (approx. mol.

It had pH 9.7 and viscosity 7 cps.

The inks described in these Examples write well on both coated anduncoated paper, and other materials, without splattering or bleeding andalso exhibit excel lent non-clogging characteristics.

We claim:

1. A low-viscosity ink designed for use in a low-- pressure writingsystem comprising a major proportion of water containing 20 to 35percent by weight ethylene glycol monomethyl ether, a water-solublecoloring agent and a water-soluble resin selected frompolyvinylpyrrolidone and polyethylene oxide, the amount ofpolyvinylpyrrolidone being 0.1 to 5 percent by weight and the amount ofpolyethylene oxide being 0.01 to 0.3 percent by weight.

2. The ink of claim 1 wherein the water-soluble resin is polyethyleneoxide.

3. The ink of claim 1 which further comprises phenol in an amounteffective to kill bacteria in said ink.

4. The ink of claim 3 wherein the phenol is present in an amount of 0.01to 0.5 percent by weight of the ink composition.

1. A LOW-VISCOSITY INK DESIGNED FOR USE IN A LOW-PRESSURE WRITING SYSTEMCOMPRISING A MAJOR PROPORTION OF WATER CONTAINING 20 TO 35 PERCENT BYWEIGHT ETHYLENE GLYCOL MONOMETHYL ETHER, A WATER-SOLUBLE COLORING AGENTAND A WATERSOLUBLE RESIN SELECTED FROM POLYVINYLPYRROLIDONE ANDPOLYETHYLENE OXIDE, THE AMOUNT OF POLYVINYLPYRROLIDONE BEING 0.1 TO 5PERCENT BY WEIGHT AND THE AMOUNT OF POLYETHYLENE OXIDE BEING 0.01 TO0.03 PERCENT BY WEIGHT.
 2. The ink of claim 1 wherein the water-solubleresin is polyethylene oxide.
 3. The ink of claim 1 which furthercomprises phenol in an amount effective to kill bacteria in said ink. 4.The ink of claim 3 wherein the phenol is present in an amount of 0.01 to0.5 percent by weight of the ink composition.